The instructions tell you that the servo should be connected to the throttle arm such that the mid-position of the throttle is at 50% throttle. The full and minimum throttle positions are dictated by the implementation of the carb. It's simple enough to reverse the throttle servo from the transmitter, but you must arrange things such that the carb is closed when the throttle stick is closest to you, and the carb is fully open when the throttle stick is in the position farthest from you when the transmitter is setting on the table. Do you still have any questions?